Sensitive photographic element for use in the silk screen process



Aug. 3, 1954 CKEL 2,685,510

E. C. YA SENSITIVE PHOTOGRAPHIC ELEMENT FOR USE IN THE SILK SCREENPROCESS Filed NOV. 14, 1951 51L VEE HALIDE EM UL SION CONTAININGCOLLOIDAL 51L VER fSIL v51? HALIDE EMULSION EDWARD 6. YAGKEL JNVENTOR.

m 3 fifi 2 A 'rTbRNEYs Patented Aug. 3, 1954 2,685,510 SENSITIVEPHOTOGRAPHIC ELEMENT FOR 'USE IN THE SILK Edward C. Yackel,

Eastman Kodak SCREEN PROCESS Rochester, N. Y., assignor to Company,Rochester,

N. Y., a

corporation of New Jersey Application November 14, 1951, Serial No.256,243

3 Claims.

This invention relates to photography and particularly to a sensitivephotographic element for use in the silk screen process.

Silk screen processes in which an image is formed photographically in abichromated gelatin layer by exposure and washing to form a reliefimage, and the image then transferred to a silk screen to form thedesired printing element are well known. Silver halide emulsions may beused in place of the bichromatecl gelatin and the relief image formed invarious ways such as by tanning development or tanning bleach andwashing out the unhardened portions, or by use of an etch bleachsolution as described in British Patent 587,957. In any of these casesthe relief image is transferred to the silk screen and the supportremoved to form the printing screen.

It is also possible to incorporate a tanning developing agent such as4-phenyl catechol in the silver halide emulsion, develop the exposedemulsion and form a relief image therein and then transfer the reliefimage to a silk screen. This material is useful for some processes butex posure is limited to some extent by the hardness of the tanned layerwhich will adhere satisfactorily to the screen. That is, the exposuremust be limited in those areas which are not critical to exposure as faras subject matter is concerned because overexposure may cause too muchphysical hardness of the tanned gelatin even though this effect isminimized by the gelatin to silver halide ratio in the preparation.Since the exposure must be limited in these areas to keep physicalhardness down to a usable level, other areas which require more exposurefor optimum results are adversely affected.

It is, therefore, an object of the present invention to provide animproved sensitive material for use in the silk screen process. Afurther object is to provide a novel photographic element. Other objectswill appear from the following description of my invention.

These objects are accomplished by using as the sensitive element adouble coated silver halide emulsion layer, the outer emulsion beingabout half the thickness of the inner emulsion and containing yellowcolloidal silver or other non-wandering yellow dye or pigment dispersedtherein.

The drawing shows in sectional view a sensitive element constructedaccording to the preferred embodiment of my invention.

The photographic element according to my invention is prepared asfollows:

A support of cellulosic material such as cellu lose acetate 0.003 inchthick was coated with a silver halide gelatin emulsion of photographicprinting paper speed. It may be modified by the incorporation of opticalsensitizers or other addenda. Such emulsions are disclosed in EdersHandbuch der Photographic. One kilogram of this emulsion containing onemole of silver per i.2 kilograms of emulsion was added to 180 grams of alow viscosity, low physical strength gelatin. The emulsion and drygelatin were mixed and melted at 40 C. When melted, 200 grams of anaqueous resin dispersion prepared as follows were added to the gelatinemulsion.

A commercial ethyl acrylate monomer was washed free of inhibitor by fourshort washes with one-tenth its weight of aqueous 5% sodium hydroxidesolution followed by four short washes with water, and a commercialacrylonitrile was distilled to remove inhibitor. Five kilograms of theethyl acrylate and 528.3 grams of the acrylonitrile were mixed in a 22liter flask, 200 grams of an alkyl aryl polyether sulfonate (Triton 720)and 33.3 grams of potassium persulfate were dissolved in 5 kilograms ofdistilled water and the temperature was brought to 55 C. Stirring wasbegun and continued throughout the reaction. About 200 cc. of the mixedmonomers were added. After five minutes and every fifteen minutesthereafter was added 25 cc. of a solution of 16.7 grams of sodiumbisulfite dissolved in 200 cc. of distilled water. The rest of themixture of monomers was added continuously with adjustment of a bathtemperature to maintain a polymerization temperature of 50 to C. Afterall of the monomer was added the contents of the flask were cooled to 30C., filtered through cloth and 700 grams of Triton 720 added to adjustthe concentration of dispersing agent on a dry weight base to 2.2% ofthe total weight. The pH was adjusted to pHQ by addition of 1 Normalsodium hydroxide.

In addition to the 200 grams of aqueous resin dispersion, 200 grams ofan aqueous dispersion of 4-phenyl catechol in gelatin solution,containing the following ingredients were added:

The first emulsion coat was spread over square feet of base and a secondemulsion coat of the same composition as the first coat but containinggrams of colloidal silver dispersion in approximately 1580 grams ofemulsion, was spread over 300 square feet of the first coat. Thecolloidal silver dispersion was prepared as follows:

The colloidal silver dispersion was prepared by the Carey Lea dextrinmethod, as modified by Wiegel (Zeit. wiss. Photo. 24, 316 (1927)). Afterformation, the sol was dispersed in a gelatin solution, set up in arefrigerator, shredded, and washed in cold water to remove the solubleimpurities. It was then melted up and the weight adjusted with distilledwater so that the dispersion contained 238 grams of gel per mole ofsilver, and weighed 4300 grams.

In place of the ethyl acrylate and acrylonitrile used in preparing theresin. dispersion, dispersions were made with methyl acrylate as theonly monomer and also with a mixture of the methyl acryiate and ethylacrylate monomers.

After the coatings were dry the sensitive element was placed with thebase side in contact with a positive image and exposed through thepositive by means of a suitable light such as tungsten, white flame arc,etc. The exposed element was then immersed in an alkaline solution ofthe following composition:

Grams Sodium carbonate (monohydrate) 75 Sodium hydroxide 5 Sodiumsulfite 2 Water to 1 liter Development was carried out for seconds at toF. This was followed by rinsing for 30 seconds in tap water at 65 to 75F., immersion in a stop bath containing 50 grams of 28% acetic acid in 1liter of water for 30 seconds and washing in tap water at about to F.Washing was continued until the undeveloped untanned portion of thestencil was dissolved out, which took about 3 to 5 minutes.

The washed out stencil was placed with the tanned gelatin side incontact with a waterwetted silk screen and thoroughly dried. When dry,the stencil was treated from the silk side with enough chloroform to wetit thoroughly for about 1 to 2 minutes. At this time the celluloseacetate base was thoroughly swollen and softened. The base could then beeasily and chloroform evaporated in a minute or two and the screen wasthen-ready for masking and printing.

The cellulose acetate base may also be removed from the finished stencilby using heat instead of solvents to soften the base. It has been foundthat by holding the silk screen with the stencil dried on it underinfrared heaters the base softens sufiiciently to permit easy stripping.The temperature to which the base must be heated is limited on the lowerside by the temperature at which the base becomes pliable and on theupper side by the temperature at which it melts or loses its cohesion tothe extent that it falls apart. This temperature range is in theneighborhood of 275-300 F. for the cellulose acetate base used;

In the accompanying drawing which illustrates a sensitive materialconstructed according to my invention, I0 is a support of celluloseacetate or other suitable material coated with a silver halide emulsionlayer H and a silver halide emulsion layer 12 containing colloidalsilver, the emulsion layer 12 being about half as thick as the emulsionlayer II.

The method which I have described provides a very satisfactory means forforming a silk screen stencil. In my sensitive material, exposure of theemulsion is limited because of the filtering eiiect of the colloidalsilver emulsion thus permitting more exposure in the small apertureareas of the positive and effectively increasing exposure latitude. Thecolloidal silver also acts as an antihalation backing. A further resultis iat a graded area of tanned gelatin to untanned gelatin always existsexcept on very great over exposure in the colloidal silver emulsionlayer. Because of this graded area of tanned to untanned gelatin,improved adhesion of the gelatin to the screen results.

Instead of yellow colloidal silver, I may use as the coloring materialof the outer emulsion layer a non-wandering yellow dye or pigment.Chrysophenin (Schultz, Farbstofftabellen, 7th Edition, No. 726) is asuitable dye, and lead chromate is a suitable pigment.

The support for my sensitive element must be removable, and any suitablematerial, such as cellulose esters or ethers, or synthetic resins suchas polyvinyl acetate, may be employed.

It will be understood that the examples and modifications includedherein are illustrative only and that my invention is to be taken aslimited only by the scope of the appended claims.

I claim:

1'. A photographic element for use in the silk screen process,comprising a cellulosic support having thereon a gelatino-silver halideemulsion layer, and on said emulsion layer a second gelatino-silverhalide emulsionlayer of the same composition as the first emulsion layerbut containing colloidal silver dispersed therein, both emulsion layerscontaining a dispersion of a tanning developing agent.

2. The element of claim 1, in which the emulcleanly stripped from thestencil. The residual 5 sion layers contain dispersion of 4'pheny1 Catechol as a tanning developing agent.

3. The element of claim 1, in which the emulsion layers contain adispersion of l-phenyl catechol in dibutyl phthalate, and the secondemulsion layer is approximately half the thickness of the first emulsionlayer.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,143,786 Mannes et al. Jan. 10, 1939 2,219,987 Gaspar Oct.29, 1940 2,219,938 Gaspar Oct. 29, 1940 2,320,693 Yauck et al June 1,1943 2,415,624 Brown et al Feb. 11, 1947 2,500,877 Sharples Mar. 14,1950

1. A PHOTOGRAPHIC ELEMENT FOR USE IN THE SILK SCREEN PROCESS, COMPRISINGA CELLULOSIC SUPPORT HAVING THEREON A GELATINO-SILVER HALIDE EMULSIONLAYER, AND ON SAID EMULSION LAYER A SECOND GELATINO-SILVER HALIDEEMULSION LAYER OF THE SAME COMPOSITON AS THE FIRST EMULSION LAYER BUTCONTAINING COLLOIDAL SILVER DISPERSED THEREIN, BOTH EMULSION LAYERSCONTAINING A DISPERSION OF A TANNING DEVELOPING AGENT.